Clearing The Filter Cache In Drupal

26th June 2009 - 3 minutes read time

Note: This post is over a year old and so the information contained here might be out of date. If you do spot something please leave a comment and we will endeavour to correct.

Filters are used in Drupal to change the content of the text of a node when it is viewed. The important thing to note is that Drupal filters should never alter the actual content of the node itself. Instead, when a node is saved it stores the output of the filter in the cache_filter table and displays this content the next time the node is viewed. This is useful because it doesn't mess about with the original text, and it speeds up the displaying of the node by running the filters once, rather than every time the node is loaded.

However, there is one thing that you should watch out for when creating your own modules. If you are using any data from other tables in your filters then you will need to clear the cache when this data changes.

Lets take a real world example where we have a filter that allowed us to automatically filter taxonomy terms in a particular vocabulary within our node content and create links around them. When the node is saved we would have a cached version of the node that would contain a few links. The problem arises when we change any vocabulary information (like adding or deleting terms). The links would still be present in our content, even though the term has been removed.

Drupal provides a hook that allows you to catch any actions that occur upon the taxonomy, this is called hook_taxonomy() and has the following structure.

function hook_taxonomy($op, $type, $array = array()){
}

We only need to intercept any action with terms, so we first make sure that the type is a term. We have previously set a variable called mycustommodule_vocabulary, and we use this to filter by a single vocabulary, rather than everything, so the next step is to run a check for this. Finally, we run an SQL query that deletes everything from the cache_filter table, which effectively clears the filter cache.

function mycustommodule_taxonomy($op, $type, $array = array()){
    switch($type){
        case 'term':
            $vid = variable_get("mycustommodule_vocabulary", '1');
            if ( $vid == $array['vid'] ) {
                // If a term has been altered within our selected vocab then delete the filter cache.
                db_query('DELETE FROM {cache_filter};');
            }
            break;
    }
}

Note that this might be a little intensive on large sites with lots and lots of nodes, especially if you are doing a lot of term editing.

PHP

Add new comment

Related Content

Installing SimpleSAMLphp Using Composer

Security Assertion Markup Language (SAML) is a standard that passes authentication credentials between hosts and essentially allows for a single sign on solution to be created. The standard uses XML files that get passed between the authentication system (known as the identity provider or IdP) and the service users want to sign into (known as the service provider or SP).

Create Checksums Using The Luhn Algorithm In PHP

The Luhn algorithm was created by Hans Peter Luhn and is a way of creating a simple checksum for a number. This algorithm, also known as the mod 10 algorithm, is used in a wide variety of applications but is commonly associated with credit card numbers.

If you look at the numbers on the front of your credit card the last digit on the right is the checksum. An algorithm is done on the other numbers and if the checksum is the same then the number is considered valid.

Swapping Between Different Composer Versions

I had an issue I was trying to debug today and needed a way to swap between different versions of composer. Composer is one of the few things that I install globally so it was locked at a particular version on the machine I was using. There has been some significant changes between version 1 and version 2 and it isn't quite safe to use a composer 2 package on a platform that has composer 1 installed. As some projects I'm working on haven't been upgraded yet I needed a way to swap between versions whilst this work was being done.

Creating A Game With PHP Part 4: Side Scrolling Shooter

As another step up from the game of snake I created in my last post I decided to try my hand at creating a side scrolling shooter. Just like my other posts, this is an ASCII based game played on the command line.

A side scrolling shooter, if you didn't already know, moves a scene from right to left across the screen with enemies moving with the scene towards the player's ship, which is on the left hand side of the scene. The player can fire bullets towards the enemies so remove them from the scene.

Seeding Random Numbers in PHP

Computers are not that great at creating random numbers as the methods they use are deterministic. That is, they start from a number (called a seed) and apply maths to that number to generate pseudorandom numbers. Most random numbers generated by computers programs use a seed provided by the system, which is generally the current time. If you can guess the initial value then you can start to work out what the random sequence of numbers generated is. Most random numbers, are therefore not suitable for encryption.

PHP: Find An Array Sequence In An Array

I was looking for a function that searched an array for another array, and after not finding one I decided to write it. What I was looking for was a function that took a smaller array and searched for that exact sequence of items in a larger array. As it happens, PHP does have a number of array search functions, but they didn't produce the correct result.